Energy and Sustainability Publications

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https://hdl.handle.net/1813/14127

This is a collection of publications from the KAUST-Cornell Center for Energy and Sustainability.

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Now showing 1 - 10 of 79

Efficient CO2 Sorbents Based on Silica Foam with Ultra-large Mesopores
Qi, Genggeng; Fu, Liling; Choi, Brian Hyun; Giannelis, Emmanuel P. (Energy & Environmental Science, 2012-04-19)
A series of high-capacity, amine impregnated sorbents based on a cost-effective silica foam with ultra-large mesopores is reported. The sorbents exhibit fast CO2 capture kinetics, high adsorption capacity (of up to 5.8 mmol g−1 under 1 atm of dry CO2), as well as good stability over multiple adsorption–desorption cycles. A simple theoretical analysis is provided relating the support structure to sorbent performance.
Effects of Bonding Types and Functional Groups on CO2 Capture using Novel Multiphase Systems of Liquid-like Nanoparticle Organic Hybrid Materials
Lin, Kun-Yi Andrew; Park, Ah-Hyung Alissa (Environmental Science & Technology, 2011-06-15)
Novel liquid-like nanoparticle organic hybrid materials (NOHMs) which possess unique features including negligible vapor pressure and a high degree of tunability were synthesized and their physical and chemical properties as well as CO2 capture capacities were investigated. NOHMs can be classified based on the synthesis methods involving different bonding types, the existence of linkers, and the addition of task-specific functional groups including amines for CO2 capture. As a canopy of polymeric chains was grafted onto the nanoparticle cores, the thermal stability of the resulting NOHMs was improved. In order to isolate the entropy effect during CO2 capture, NOHMs were first prepared using polymers that do not contain functional groups with strong chemical affinity toward CO2. However, it was found that even ether groups on the polymeric canopy contributed toCO2 capture in NOHMs via Lewis acid base interactions, although this effect was insignificant compared to the effect of task-specific functional groups such as amine. In all cases, a higher partial pressure of CO2 was more favorable for CO2 capture, while a higher temperature caused an adverse effect. Multicyclic CO2 capture tests confirmed superior recyclability of NOHMs and NOHMs also showed a higher selectivity toward CO2 over N2O, O2 and N2.
Dynamics of Solvent-free Grafted Nanoparticles
Chremos, Alexandros; Panagiotopoulos, Athanassios; Koch, Donald (The Journal of Chemical Physics, 2012-01-26)
The diffusivity and structural relaxation characteristics of oligomer-grafted nanoparticles have been investigated with simulations of a previously proposed coarse-grained model at atmospheric pressure. Solvent-free, polymer-grafted nanoparticles as well as grafted nanoparticles in a melt were compared to a reference system of bare (ungrafted) particles in a melt. Whereas longer chains lead to a larger hydrodynamic radius and lower relative diffusivity for grafted particles in a melt, bulk solvent-free nanoparticles with longer chains have higher relative diffusivities than their short chain counterparts. Solvent-free nanoparticles with short chains undergo a glass transition as indicated by a vanishing diffusivity, diverging structural relaxation time and the formation of body-centered-cubic-like order. Nanoparticles with longer chains exhibit a more gradual increase in the structural relaxation time with decreasing temperature and concomitantly increasing particle volume fraction. The diffusivity of the long chain nanoparticles exhibits a minimum at an intermediate temperature and volume fraction where the polymer brushes of neighboring particles overlap, but must stretch to fill the interparticle space.
Dynamics in Coarse-grained Models for Oligomer-grafted Silica Nanoparticles
Hong, Bingbing; Chremos, Alexandros; Panagiotopoulos, Athanassios (The Journal of Chemical Physics, 2012-05-30)
Coarse-grained models of poly(ethylene oxide) oligomer-grafted nanoparticles are established by matching their structural distribution functions to atomistic simulation data. Coarse-grained force fields for bulk oligomer chains show excellent transferability with respect to chain lengths and temperature, but structure and dynamics of grafted nanoparticle systems exhibit a strong dependence on the core-core interactions. This leads to poor transferability of the core potential to conditions different from the state point at which the potential was optimized. Remarkably, coarse graining of grafted nanoparticles can either accelerate or slowdown the core motions, depending on the length of the grafted chains. This stands in sharp contrast to linear polymer systems, for which coarse graining always accelerates the dynamics. Diffusivity data suggest that the grafting topology is one cause of slower motions of the cores for short-chain oligomer-grafted nanoparticles; an estimation based on transition-state theory shows the coarse-grained core-core potential also has a slowing-down effect on the nanoparticle organic hybrid materials motions; both effects diminish as grafted chains become longer.
Diffusivities, viscosities, and conductivities of solvent-free ionically grafted nanoparticles
Hong, Bingbing; Panagiotopoulos, Athanassios (Soft Matter, 2013-05-28)
A new class of conductive composite materials, solvent-free ionically grafted nanoparticles, were modeled by coarse-grained molecular dynamics methods. The grafted oligomeric counterions were observed to migrate between different cores, contributing to the unique properties of the materials. We investigated the dynamics by analyzing the dependence on temperature and structural parameters of the transport properties (self-diffusion coefficients, viscosities and conductivities) and counterion migration kinetics. Temperature dependence of all properties follows the Arrhenius equation, but chain length and grafting density have distinct effects on different properties. In particular, structural effects on the diffusion coefficients are described by the Rouse model and the theory of nanoparticles diffusing in polymer solutions, viscosities are strongly influenced by clustering of cores, and conductivities are dominated by the motions of oligomeric counterions. We analyzed the migration kinetics of oligomeric counterions in a manner analogous to unimer exchange between micellar aggregates. The counterion migrations follow the “double-core” mechanism and are kinetically controlled by neighboring-core collisions.
Diffusive Dynamics of Nanoparticles in Aqueous Dispersions
He, Kai; Spannuth, Melissa; Conrad, Jacinta; Krishnamoorti, Ramanan (Soft Matter, 2012-10-04)
The diffusive dynamics of 100 nm to 400 nm diameter polystyrene nanoparticles dispersed in water were studied using brightfield and fluorescence based differential dynamic microscopy (DDM) and compared to those obtained from dynamic light scattering. The relaxation times measured with brightfield and fluorescence DDM over a broad range of concentration of nanoparticles (10−6 ≤ φ ≤ 10−3) and scattering vectors (0.5 μm−1 < q < 10 μm−1) are in excellent agreement with each other and extrapolate quantitatively to those obtained from DLS measurements. The diffusion coefficients extracted from the q-dependent relaxation times using all three methods are independent of the nanoparticle concentration.
Deposition of LDH on Plasm Treateed Polylactic Acid to Reduce Water Permeability
Bugatti, Valeria; Livi, Sebastien; Hayrapetyan, Suren; Wang, Yue; Estevez, Luis; Vittoria, Vittoria; Giannelis, Emmanuel (Journal of Colloid and Interfcae Science, 2013-04-04)
A simple and scalable deposition process was developed to prepare polylactic acid (PLA) coatings with enhanced water barrier properties for food packaging applications. This method based on electrostatic interactions between the positively charged layers of layered double hydroxides (LDHs) modified with ionic liquids (ILs) and the negatively charged plasma treated polylactic acid leads to homogeneous, stable, and highly durable coatings. Deposition of the LDH coatings increases the surface hydrophobicity of the neat PLA, which results to a decrease in water permeability by about 35%.
Crowded, Confined, and Frustrated: Dynamics of Molecules Tethered to Nanoparticles
Agarwal, Praveen; Kim, Sung A; Archer, Lynden (Physical Review Letters, 2012-12-19)
Above a critical chemistry-dependent molecular weight, all polymer molecules entangle and, as a result, exhibit slow dynamics, enhanced viscosity, and elasticity. Herein we report on the dynamics of low molecular weight polymers tethered to nanoparticles and find that even conventionally unentangled chains manifest dynamical features similar to entangled, long-chain molecules. Our findings are shown to imply that crowding and confinement of polymers on particles produce topological constraints analogous to those in entangled systems.
Chloride Adsorption by Calcined Layered Double Hydroxides in Hardened Portland Cement Paste
Yoon, Seyoon; Moon, Juhyuk; Bae, Sungchul; Duan, Xiaonan; Giannelis, Emmanuel; Monteiro, Paulo (Materials Chemistry and PHysics, 2014-02-13)
This study investigated the feasibility of using calcined layered double hydroxides (CLDHs) to prevent chloride-induced deterioration in reinforced concrete. CLDHs not only adsorbed chloride ions in aqueous solution with a memory effect but also had a much higher binding capacity than the original layered double hydroxides (LDHs) in the cement matrix. We investigated this adsorption in hardened cement paste in batch cultures to determine adsorption isotherms. The measured and theoretical binding capacities (153 mg g−1 and 257 mg g−1, respectively) of the CLDHs were comparable to the theoretical capacity of Friedel's salt (2 mol mol−1 or 121 mg g−1), which belongs to the LDH family among cementitious phases. We simulated chloride adsorption by CLDHs through the cement matrix using the Fickian model and compared the simulation result to the X-ray fluorescence (XRF) chlorine map. Based on our results, it is proposed that the adsorption process is governed by the chloride transport through the cement matrix; this process differs from that in an aqueous solution. X-ray diffraction (XRD) analysis showed that the CLDH rebuilds the layered structure in a cementitious environment, thereby demonstrating the feasibility of applying CLDHs to the cement and concrete industries.
Chemical Engineering in the Electronics Industry: Progress Towards the Rational Design of Organic Semiconductor Heterojunctions
Clancy, Paulette (Current Opinion in Chemical Engineering, 2012-05-04)
Design of the heterojunction in all-organic solar cells is a critical aspect of understanding and controlling charge transport characteristics. The use of multiscale computational approaches has an important role to play in heterojunction design. Ordered heterojunctions offer promising routes to finesse issues that impede charge transport in bulk heterojunctions. The future is likely to lay in the development of multi-junction devices where computational insight is likely to help guide experimental searches for optimal interface design.

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